I'm thinking about getting a HRM for statics and breathe-up-type practice. Not sure how one even works but I'm guessing it has some sort of sensor that picks up your wrist pulse. Does anyone have a HRM they wear WHILE diving (or is it even possible)? I found one on eBay that is waterproof but it says the sensor will be inaccurate "while submerged". I wonder if this means "while wet" or "at depth"... I'm not TOO interested in my HR at depth, but I'd like to look at it while I'm floating and breathing up for the dive.